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More Moon and Jupiter

The planet Jupiter huddles close to the lower right of the Moon early this evening. To the eye alone, Jupiter looks like a brilliant star — it outshines all the true stars in the night sky.

A bit of help reveals much more about the giant planet. Binoculars show us Jupiter’s four largest moons: Io, Europa, Ganymede, and Callisto. They look like small stars lining up close to the planet. And just about any telescope reveals the planet’s cloud bands and its ruddy “eye” — the Great Red Spot.

But some things you can’t see even with a telescope. That includes Jupiter’s rings — bands of dust and rock around the planet. Although they span close to 150,000 miles, they’re so sparse that they weren’t even discovered from Earth. Instead, they were first seen by the twin Voyager spacecraft when they flew past Jupiter in 1979.

Since then, we’ve seen the rings with other spacecraft, as well as with some of the most powerful telescopes on Earth.

There are four major ring components. There’s the main ring, which is the brightest of the bunch. Much of its material consists of bits of rock. Between the main ring and Jupiter’s cloudtops is the halo — a big doughnut of dust. And outside the main ring are the two gossamer rings, which are also dusty.

All of the rings are kept in place by small moons. They’re also supplied by the moons. Space rocks hit the moons and blast out debris. Over time, the debris spreads out — forming Jupiter’s hard-to-see rings.

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